1. Field of the Invention.
The present invention relates to an apparatus and method for enhancing the power output of a free electron laser (FEL). More particularly the present invention relates to changing the wave amplification resonance condition along the length of the interaction region between the electron beam and the applied magnetic field.
2. Description of the Prior Art.
In construction of a FEL it is highly desirable to continuously change the wave amplification resonance condition of an electron interacting with a pump field along the length of the interaction region to enhance the amount of electron kinetic energy that can be converted to laser radiation. Techniques within prior art have been developed to perform this continuous change when the resonance condition is sensitive to changes in the magnitude of the pump wave magnetic field intensity, or when the period of the pump wave can be continuously decreased as the electron passes through the interaction region. There are, however, cases in which the effects described above as produced by either of the defined techniques are too small to be practically implemented. For these and other similar cases the present invention provides a technique producing significant effects whereby the local resonance conditions can be continuously changed along the laser interaction region by using a static transverse magnetic field having a longitudinal magnetic field gradient.